Increasing numbers of Twitterers don’t even pretend to be human. Or worse, do pretend, when they are actually bots—tiny, skeletal, incapable robots, usually little more than a few crude lines of computer code. The scary thing is how easily we can be fooled.

What is MagnaCarta worth? Exactly $21,321,000. We know because that’s what it fetched in a fair public auction at Sotheby’s in New York. Twenty-one million is, by far, the most ever paid for a page of text, and therein lies a paradox: Information is now cheaper than ever and also more expensive. Mostly, of course, information is practically free, easier to store and faster to spread than our parents imagined possible. In one way, Magna Carta is already yours for the asking: you can read it any time, at the touch of a button. It has been preserved, photographically and digitally, in countless copies with no evident physical reality, which will nonetheless last as long as our civilization. In another way, Magna Carta is a 15-by-17-inch piece of parchment, fragile and scarce and practically unreadable. Why should that version be so valuable? Magna Carta itself is a nice reminder of how costly it once was to store and spread information. Its very purpose was to get the king’s word down in tangible form, safeguard it, …